1. Field of the Invention
The field of this invention is clutches and more particularly clutches for screw guns.
2. Description of Related Art
The prior art includes several examples of positive disengagement clutches, or xe2x80x9cquietxe2x80x9d clutches. Generally, these clutches include some mechanism for moving one of the clutch surfaces away from the other clutch surface when they disengage in order to prevent the clutch surfaces from clashing against one another.
U.S. Pat. Nos. 4,655,103, 4,809,572, and 4,947,714 are three examples each disclosing a quiet clutch for a screw gun. The ""714 patent discloses a clutch with three clutching elementsxe2x80x94a drive element, an intermediate element, and an output element. To drive a screw, all three clutch elements are initially engaged with one another (see FIG. 2 of the ""714 patent). At some point while driving the screw, torque causes the intermediate element and the output element to separate from each other due to the cam surfaces 30, 15 (see FIG. 3 of the ""714 patent). When the screw is almost driven to its intended depth, the intermediate element and the output element slide axially forward away from the input element, following the screw into the work piece (see FIG. 4 of the ""714 patent). When the screw reaches its intended depth, the input element and the intermediate element slip. Once the slip occurs, the torque is released and the separation between the output element and the intermediate element caused by the torque and the cam surfaces 30 and 15 is no longer present. A spring positioned between the input element and the intermediate element returns the intermediate element back together with the output element. This return creates a gap xe2x80x9csxe2x80x9d between the input element and the intermediate element (see FIG. 5 of the ""714 patent). The gap prevents clashing of the clutch surfaces during disengagement.
While the clutch described in the ""714 patent prevents clashing of the clutch surfaces during disengagement, the contact area between the intermediate element and the output element in the ""714 patent decreases as the intermediate element moves away from the output element. This decrease in the contact area leads to an additional increase in the stress which arises on the intermediate element and the output element from the transfer of torque from one to the other. The increased stress can lead to a decrease in the fatigue life of each part.
It is a feature of the present invention to provide a clutch which prevents clashing of the clutch surfaces during disengagement and which is also simple and inexpensive. It is also a feature of the invention to provide a retaining ring which extends circumferentially around a first spindle in a clutch to limit the movement of a first clutch supported on the first spindle for axial and rotational movement relative thereto.
In an embodiment of the invention, a screw gun comprises a drive means, a first spindle having a first helical spline formed on a portion thereof, a first clutch having a second helical spline formed on a portion thereof so that the second helical spline engages the first helical spline of the first spindle, the first clutch being movable rotationally and axially relative to the first spindle, and a second spindle, one of the first spindle or the second spindle being driven by the drive means. A bit adapted for driving a fastener into a work piece is operatively connected to the other of the first spindle or the second spindle. A second clutch is mounted on the second spindle and rotationally fixed relative to the second spindle, the second clutch being movable in an axial direction relative to the first spindle to engage the first clutch, torque being transmittable between the first clutch and the second clutch upon engagement with one another. A spring biases the first clutch and the second clutch apart. When torque is being transmitted to the fastener in at least one direction, an axial reaction force is created between the first and second helical splines which moves the first clutch axially towards the second clutch causing the first clutch to rotate relative to the first spindle.
In another embodiment of the invention, a clutch comprises a first spindle having a first complementary engaging surface formed on an exterior cylindrical surface thereof, a first clutch having a second complementary engaging surface formed on an interior bore thereof, the first clutch supported on the first spindle at the interior bore for rotational and axial movement relative to the first spindle, with the first and second complementary engaging surfaces in engagement, and a second spindle, one of the first spindle or the second spindle being adapted to be driven by a drive means. A second clutch is mounted on the second spindle and rotationally fixed relative to the second spindle, the second clutch being movable in an axial direction relative to the first spindle to engage the first clutch, and torque being transmittable between the first clutch and the second clutch upon engagement with one another. A spring biases the first clutch and the second clutch apart. When torque is being transmitted between the first spindle and the first clutch in at least one direction, an axial reaction force is created between the first and second complementary engaging surfaces which moves the first clutch axially towards the second clutch causing the first clutch to rotate relative to the input spindle.
In another embodiment of the invention, a method of driving a fastener comprises the steps of pushing a fastener against a work piece with a screw gun which causes a first clutch and a second clutch to engage, driving the fastener into the work piece by transferring torque between the first clutch and the second clutch and then to the fastener, causing the torque which is being transferred between the first clutch and the second clutch to act upon helical splines positioned between the first clutch and a first spindle creating an axial reaction force, the axial reaction force in turn creating a small clearance distance between the first clutch and the first spindle, and disengaging the first clutch and the second clutch when the fastener is driven to the desired depth while simultaneously removing the first clearance distance between the first clutch and the first spindle and creating a second clearance distance between the first clutch and the second clutch.
In another embodiment of the invention, a clutch for a screw gun comprises a first spindle, a first clutch supported on the first spindle for rotational and axial movement relative thereto, and a second spindle, one of the first spindle or the second spindle being adapted to be driven by a drive means, the other of the first spindle or the second spindle being adapted to drive a fastener. A second clutch is attached to the second spindle for rotation therewith, the second clutch adapted to engage the first clutch and transfer torque. A retaining ring extends circumferentially around the first spindle, the retaining ring abutting a surface of the first clutch when the first clutch moves axially on the first spindle wherein the axial movement of the first clutch relative to the first spindle is limited by the retaining ring.
These and other objects, features and advantages of the invention are apparent through the detailed description of the preferred embodiments and the drawings.